Recent advances in the size and performance of micro-electromechanical systems (MEMS)-based inertial instruments enable the development of a balance prosthesis to provide feedback regarding head orientation to patients with chronic balance dysfunction. There is a need for balance prostheses to assist patients with such chronic balance disorders, as well for devices that can facilitate rehabilitation of such disorders through training. The one-piece, noninvasive, and discreet BALCAP prosthesis proposed herein offers the potential to satisfy both requirements via a simple, adjustable or presized hat, available in different styles/colors. With the BALCAP prosthesis, low-amplitude vibrotactile cues are provided directly to the head via hatband tactors that furnish the wearer with feedback concerning head tilt in the pitch and roll planes, whether he/she is stationary or moving. To evaluate the utility of the proposed BALCAP balance prosthesis, patients with chronic balance dys- function spanning a range of etiologies (e.g., peripheral dysfunction, central dysfunction, and multi-factorial disequilibrium, also referred to as disequilibrium of aging) will undergo postural stability and gait assessments to determine if the device offers: (1) assistive benefit;i.e., significantly improves assessment scores when the BALCAP is enabled vs. disabled;and (2)rehabilitation benefit;i.e., yields significantly-improved assessment scores when the BALCAP is disabled (turned off) following 6 weeks of rehabilitation training with the device enabled. Regarding the first hypothesis, prior work by the proposing team demonstrated significant assistive improvements in postural stability in patients with bilateral vestibular loss (BVL) based on a first-generation head-mounted vibrotactile prosthesis. The proposed work will evaluate the assistive efficacy of such a balance prosthesis in a population of chronic imbalance patients spanning a wider range of disease etiologies than was addressed in the prior study, the inclusion of which will greatly expand the size of the commercial market. Concerning the second hypothesis, published findings from one research group supports the notion that rehabilitation training using such a substitute sensory channel can lead to post-training retention of residual balance improvement. However, directly contradictory findings-at least concerning BVL patients-have been published by an independent group. To reconcile these disparate outcomes, the work proposed herein will also investigate the rehabilitative potential of the BALCAP device based on a 6-week structured training regimen that includes both static and dynamic exercises. If rehabilitative training to achieve residual balance retention is possible, expanding training to include both static and dynamic activities is most likely to make it evident. If the hypothesis concerning the assistive benefit is supported, a head-mounted vibrotactile prosthesis product would enable immediate benefit to be provided to a large number of patients with chronic postural instability. If rehabilitative training to achieve residual balance retention is possible, it would open new areas of research, such as how to optimize training to maximize residual retention of balance improvements. PUBLIC HEALTH RELEVANCE: Products resulting from this research are anticipated to offer significant benefit to patients with chronic postural instability to help them improve their balance in both static and dynamic activities, allowing them to function more normally. The availability of a simple, one-piece, noninvasive, discreet, and low-cost balance prosthesis will enhance the quality of life for balance-disordered patients and could lead to further advancements in this area. The use of such a device as an assistive aid, both inside and outside of the home, could yield both immediate (assistive) and longer-term (rehabilitation) benefits. An assistive prosthesis might also allow patients to "train" while performing their normal activities (in contrast to structured exercises), substantially reducing patient burden.